The present invention relates to a windshield for a weighing apparatus such as an electronic scale, and particularly to a windshield including a sliding door in a windshield side portion.
In a weighing apparatus, so-called electronic scales including an electromagnetic balancing type weighing apparatus that is called an electronic balance and a high-precision load cell type scale can measure a micro mass, while the electronic scales are largely affected by disturbance. One of the disturbances is airflow around a pan on which a measurement target is placed.
For example, airflow from an air conditioner, human breath during the measurement, and airflow generated by human walk act as a wind pressure on a weight-bearing portion centered on the pan, and the pan is affected by a so-called blast of the wind pressure, which results in an unstable measurement value and a measurement error. Therefore, a windshield that covers the weight-bearing portion centered on the pan is used not only in a high-precision electronic scale called an analytical balance having a minimum scale of about 0.1 mg but also in a model commonly called a general-purpose balance whose minimum scale ranges from about 0.01 g to about 0.001 g.
For the analytical balance, because the windshield is an element necessary to accurately measure a weight, the windshield is formed as part of the electronic scale, that is, the windshield is integral with the electronic scale main body. On the other hand, for the general-purpose balance, frequently the detachable windshield that is formed independently of the electronic scale main body is used in the electronic scale if needed.
In the analytical balance, the windshield integral with the electronic scale main body has an opening and closing portion (hereinafter referred to as “door”) in right and left portions or an upper portion of the windshield, and good usability is achieved. However, the windshield portion becomes inevitably large and complicated because a frame and a door sliding portion are formed to ensure the opening and closing of the door. Frequently the detachable windshield has a structure simpler than that of the integrated windshield because of demand for light weight and low cost, and it is recognized that the detachable windshield is inevitably inferior in usability to the integrated windshield.
In the future, it is believed that the high-precision measurement is increasingly demanded not only in the analytical balance but also in the general-purpose balance. Therefore, the necessity of the windshield is increased in the whole electronic scale.
In a basic configuration of the windshield, frequently the door is formed in a windshield side portion in order to open the inside of the windshield. The whole shape of the integrated windshield frequently used in the analytical balance is often formed into a square shape such as a rectangular solid or a cubic by a flat plate such as a plate glass. In the square-shape windshield, the glass plate constituting the windshield side plate is slid in a front-back direction of the windshield to open and close the windshield.
Generally the square-shape windshield has the good operability. However, because the sliding windshield side plate is moved backward in opening the windshield, a space is required to move the windshield side plate in a rear portion of the windshield, which enlarges the configuration of the windshield. Therefore, because a weighing mechanism chamber or a board placement space is previously provided at the back of the windshield, the sliding door configuration is adopted only in the weighing apparatus such as the analytical balance having the integrated windshield in which the space can be used as a windshield side plate storage space.
One of vertical side edges of the windshield side plate is connected to the windshield main body by a hinge, and the windshield side plate is turned about the hinge to open and close the side plate, whereby the windshield side plate storage space is eliminated in opening and closing the door. However, when the door is opened and closed by turning the side plate about the hinge, a large wind pressure is generated in a space near the pan, where airflow should be avoided. Therefore, the configuration becomes countercurrent against the original purpose of the windshield, and the configuration cannot be used as the opening and closing mechanism of the windshield for a weighing apparatus.
In view of the foregoing, the whole of the windshield is formed into a substantially cylindrical shape, and at least part of a cylindrical side portion of the windshield is rotated about a cylindrical shaft center of the windshield. At this point, because the rotating portion is moved only on a circle that is a cylindrical projection, it is not necessary to provide the storage space at the back of the windshield in opening the windshield. This enables the windshield to be miniaturized.
The door is not opened and closed by turning the side plate about the hinge, but the door is opened and closed by the sliding operation. Therefore the door can sufficiently act as the windshield while the particular wind pressure is not generated in opening and closing the door.
From this standpoint, some proposals of the substantially cylindrical windshield have been made as follows:
Patent Document 1: Japanese Utility Model Application Laid-Open No. 7-054820
Patent Document 2: U.S. Pat. No. 4,798,250